In a conventional apparatus (German Pat. No. 20 45 604 which corresponds to U.S. Pat. No. 3,757,637) the angled milling head is provided with a centering ring which engages the bottom plate of the milling spindle carriage Four ball-roller elements which are arranged offset at 90.degree. are provided on the bottom plate, on which ball-roller elements is radially supported the centering ring. When the clamping elements are released, the flange of the angled milling head is spaced some distance from the bottom plate of the milling spindle carriage, so that the angled milling head can be rotated about the milling spindle axis by means of a pinion driven by the servomotor and which engages a ring gear which is provided on the centering ring. The angled milling head can in this manner be moved into four basic positions which are offset at 90.degree. through four limit switches which are distributed on the periphery. By means of an indexing device, which consists of indexing surfaces which are arranged on the flange of the angled milling head and by means of stops which cooperate therewith and can be mechanically moved into their path of movement, it is possible for the angled milling head to be adjusted slightly by rotating it about the spindle axis starting out from each of its four basic positions in one or the other direction. The indexing device is provided for the purpose of adjusting the socalled plunge of the milling tool relative to the surface of the workpiece which is to be worked. Since the indexing device is equipped with a total of five different stops, the angled milling head, starting out from each of its four 90.degree. positions, can be rotated in relatively small angle of traverse areas into each of the five different angular positions. After indexing the angled milling head, however, the flange of the angled milling head must be moved by means of the clamping elements absolutely into abutment with the bottom plate of the milling spindle carriage, since the centering ring which is relatively short in axial direction and the ball-roller elements are not suited to transmit larger radial forces or tipping forces from the angled milling head onto the milling spindle carriage. Prior to the start of each further intended rotation of the angled milling head, the clamping elements, however, must again be released, which causes the flange of the angled milling head to be lifted off from the bottom plate. In these operations, which today take place automatically, there exists the danger that dirt particles which exist near the separating line, in particular also chips, are pulled into the separating line. The result is inexactnesses, wear and loss of stiffness or preciseness of coaxial alignment in the plane of the flange connection. Blowing and wiping devices have shown only a small cleaning action, because the dirt accumulates in different consistency and the angled milling head is rotated both to the right and to the left. Because of the small stiffness of the connection between the flange of the angled milling head and the bottom plate, it is not possible to work when the clamping elements are released. This has the disadvantage that the angled milling head, during certain working operations, for example the manufacture of diagonally or circularly extending milling operations, cannot continuously rotate about the milling spindle axis.
Therefore, the basic purpose of the invention is to provide an apparatus for facilitating a rotating of a tool-receiving device, in particular an angled milling head, at the free (lower) end of a milling spindle carriage of the abovementioned type, in which the stiffness or preciseness of coaxial alignment characteristic of the connection between the tool-receiving device and the milling spindle carriage is substantially increased, so that work can be done even with the released clamping elements as well as a regulated rotating of the tool-receiving device into any desired angular position, and in which furthermore the penetration of dirt and problems connected therewith are avoided.
This purpose is attained according to the invention by securing in the milling spindle carriage an elongated bushing which is concentric with respect to the milling spindle axis and which at its free (lower) end has a conical surface defining a receiving opening, by rotatably supporting in the bushing a support sleeve by means of radial and axial bearings, which at the free (lower) end of the support sleeve a fastening flange is provided for the tool-receiving device. Above the fastening flange a centering cone is provided conforming in shape to and being received in the conical receiving opening. The centering cone is supported on the bushing by an interpositioning of an oil film therebetween. The purpose is further attained by the clamping elements being arranged between a bearing sleeve or milling spindle carriage and the support sleeve or parts connected thereto such that in the clamping position of the clamping elements, the centering cone is urged against the conical receiving opening.
Thus, the invention is based on the thought to no longer release the tool-receiving device, in particular the angled milling head, as this had been done so far during each rotating movement of the milling spindle carriage, but to connect it fixedly to a part which is supported in the milling spindle carriage, namely the support sleeve, and to design the support sleeve in such a manner that it is supported as much as possible clearance-free (i.e. no play) and as stable as possible in the milling spindle carriage, so that, if desired, work can be done when the clamping elements are released. The support sleeve is for this purpose supported in an elongated bushing, the axial length of which is great in relationship to its diameter. In order to achieve the desired precise tolerance (i.e. no play) a cone is provided on the support sleeve and through the interpositioning of a thin oil film maintains a uniform abutting relation with the conical receiving opening. This occurs when the clamping elements are released due to the provision of an axial sliding bearing having very precise axial tolerances. Preferably all bearings which are provided between the bushing and the support sleeve, including the bearing between the conical receiving opening and the centering cone are constructed as hydrostatic sliding bearings.
The inventive development substantially increases the stiffness or preciseness in the holding of the coaxial relation of the connection between the tool-receiving device (angled milling head) and the milling spindle carriage. By increasing this stiffness and the practical close tolerance between the support sleeve and the bushing it is possible for certain working operations to rotate the support sleeve with the tool-receiving device secured thereon, for example controlled by a NC-control, into any desired angular position which is required by the working task, for example for diagonal milling. If such a rotating of the angled milling head during the working task is not necessary, then the clamping elements can be moved into the clamping position and through this a better connection between the milling spindle carriage and the tool-receiving device can be created. Due to the possibility of rotating the tool-receiving device during the working task about the milling spindle axis, it is also possible to design the tool-receiving device simpler and more compact. Namely socalled attachment heads exist as a tool-receiving device, which attachment heads were secured in place of an angled milling head up to now on the bottom plate of the milling spindle carriage. The attachment heads were designed such that the tool could be rotated about an axis which is coaxial with respect to the milling spindle axis and additionally yet about a horizontal axis, so that with these two rotational adjusting axes and three further linear adjusting axes of the milling machine, milling operations in three dimensions in the NC-operation were possible. Due to the inventive development of the apparatus, the rotatable support about an axis coaxial with respect to the milling spindle axis in the attachment head can be omitted. Furthermore, it must be emphasized that by avoiding an axial movement between the tool-receiving device and milling spindle carriage during rotation, the collecting of dirt, chips etc. and the problems connected therewith are avoided.